Preparation And Representation Of Antioxidant Peptide From Soy Protein

In this research, the separation of 7S and 11S soybean globulin from low-temperature defatted soybean flake by the optimized method of Nagano. Alcalase, Neutrase neutral protease, trypsin, papain and bromelain were selected to hydrolyze 7S and 11S soybean globulin for the acquirement of antioxidative peptides. The best proteinase was choosen according to the antioxidation activity of hydrolysate from globulin. The antioxidant peptide was prepared under the optimum hydrolysis conditions, and the high performance gel chromatography was used to analyze the molecular weight distribution of higher antioxidant activity of peptides.The relative purity of separated 7S and 11S soybean globulin was up to 83.68% and 87.59% respectively by SDS-PAGE electrophoresis analysis. The five kinds of proteases were selected to hydrolyze the 7S and 11S soybean globulin in their respective single-factor, and the hydrolysis time was 1hour, 2hours, 3hours, 4hours, and 5hours. In the best condition, the best proteinase was choosen according to antioxidant activity and the degree of hydrolysis in different time and the best conditon to hydrolyze 7S and 11S soybean globulin was confirmed. Hydrolysate, which was hydrolysed by Alcalase amoung five proteinases, possesses higher antioxidative activity, and the best hydrosis condition for hydrolysis of soybean globulin were:temperature was 55℃, pH was 8.0, concentration of substrate was 4%, Alcalase dosage was 5%, As the hydrolysis time extension, the hydrolyzation degree of Alcalase increased, but the antioxidative activity of hydrolysate from globulin weakened after strengthening first. The antioxidative activity of hydrolysate from globulin hydroelyzed by Alcalase was highest in 4 hours of hydrolyzation when the hydrolysates from 7S and 11S soybean globulin protection factor were 1.48 and 1.46, DPPH radical scavenging rates were 60.85% and 58.15%.Purifiction process of peptides with antioxidative activity in the hydrolysate by ultrafiltration and gel filtration chromatography. The supernatant of the hydrolysate was seperated by three kinds of ultrafiltration membranes, and four fractions of the molecular weight more than 30kDa, in the range of 10kDa-30kDa and5kDa-10kDa, and under 5kDa were obtained. The molecular weight of separation profile of the fraction under 5kDa from 7S and 11S soybean globulin were mainly in the range of 1000Da, accounting for 92.92% and 87.53%, the content of them approximately 82.6% and 89.1%. The fraction under 5kDa had the best antioxidative activity by the methods of antioxidative activity and DPPH free radical scavenging rate. The part of this fraction was purified further by Sephadex G-25 gel filtration chromatography. After that, the fraction under 5kDa from the 7S and 11S glycinin hydrolysates were divided into four groups A, B, C and D, the antioxidative activity amoung A, B, C and D were A> C> B> D.The molecular weight of sample A, which had the best antioxidant activity, was about 1068.81Da.